Field of the Invention
The present invention relates to a rotary machine configured by applying an inverter drive system to a rotary machine and a drive system for the rotary machine and, more particularly, to a rotary machine that can reduce electrical corrosion of a rotary machine bearing caused by an inverter and a drive system for the rotary machine.
Background Art
In recent years, with high control performance and an energy saving effect as a background, in many cases, rotary machine drive systems are configured by applying inverter systems to rotary machines such as an electric motor and a generator. According to the advance of an inverter series connection or parallel connection technology in recent years, it is becoming possible to drive a large-capacity rotary machine or a MW class or above.
On the other hand, a rate of change (dV/dt) of an output voltage pulse is becoming high according to a loss reducing technology for an inverter. Therefore, the problem of electrical corrosion of a rotary machine bearing cannot be ignored.
As measures against the electrical corrosion, there have been proposed, for example, a method of avoiding electrical contact by adopting a magnetically-levitated bearing, a method of applying ceramics to a bearing rather than metal, and a method of inserting a common mode filter between an inverter and a rotary machine. As an example of the measures, in Japanese Patent No. 4260110, electrical corrosion is prevented by inserting the common mode filter.
However, in the existing system, a rotary machine of a MW class or above has large rotor weight. Therefore, the size of the structure of the magnetic bearing increases, it is difficult to manufacture ceramics that can withstand the weight, and the size of the system increases because of the insertion of the common mode filter through which large electric power passes.